Interestingly, with stock Android 6 ROM that comes preinstalled with Khadas VIM Pro, TWRP does load - holding POWER and pressing RESET and releasing it, still holding POWER until USB key starts being read.

@Gouwa, @terry, maybe uboot differs between what’s on GitHub and what’s where you build stock ROM from? Can you please check it?

Just to be little hint, this version of kvim.h is included in manifest when Android Nougat is being built while following version is on Nougat branch as latest version. There are quite a number of differences between them. However, I am yet unable to spot how to make sure recovery.img is read from USB stick or SD card